1. Field of the Invention
This invention relates to a 2-fluorobenzonitrile derivative. More particularly, it relates to a 4-[trans-4-[(E)-2-(trans-4-alkylcyclohexyl)vinyl]cyclohexyl]-2-fluorobenzo nitrile and a liquid crystal composition containing the above compound as an effective component.
2. Description of the Related Art
Liquid crystal display elements utilize the optical anisotropy and the dielectric anisotropy of liquid crystal substances, and as the display mode of the elements, TN mode (twisted nematic mode), supertwisted nematic mode (STN mode), dynamic scattering mode (DS mode), guest-host mode (G-H mode), DAP mode, etc. are known. Further, as the method for driving these modes, static driving method, multiplex driving method, active matrix driving method, two-frequency driving method, etc. have been employed. The properties of liquid crystal substances used for these liquid crystal display elements are various, but any liquid crystal substances are common in the aspect of stability to moisture, air, heat, light, etc. Further, it is required for the elements that the liquid crystal phases are exhibited within a temperature range as broad as possible, around room temperature; the viscosity is low; and in the display element, a quick response rate, a high contrast and further a low driving voltage are required- Further, it is necessary that an adequate dielectric anisotropy (.increment..epsilon.) is effected depending upon the kind of display element. However, a single liquid crystal compound satisfying these characteristics has not yet been known. Thus, it is the present status that liquid crystal compositions obtained by blending several kinds of liquid crystal compounds and non-liquid crystalline compounds have been used.
Now, the following compounds similar to those of the present invention have been disclosed: ##STR2## wherein R represents an alkyl group of 1 to 8 carbon atoms and X represents a hydrogen atom or a fluorine atom.
With regard to the compound (i), no example is disclosed in the above Japanese patent application laid-open No. Sho 61-215336, and according to the study of the present inventors, the compound has drawbacks that it has a high viscosity for its dielectric anisotropy value and an inferior compatibility with other liquid crystalline compounds. Further, the compound (ii), too, has drawbacks that it has a small dielectric anisotropy value (.increment..epsilon.) and its temperature range wherein the liquid crystal phase is exhibited is narrow.
Thus, the present inventors have made extensive research in introduction of 2-fluorobenzonitrile derivative into the core structure of an alkyldicyclohexylethylene, and as a result, have invented a novel liquid crystalline substance described below, which exhibits a low viscosity and a nematic phase within a notably broad temperature range, has a high dielectric anisotropy value and a good compatibility with other liquid crystalline compounds at low temperatures.
The object of the present invention is to provide a novel liquid crystal compound having a large dielectric anisotropy value, exhibiting liquid crystal phases within a broad temperature range and having a good compatibility with other known liquid crystal compounds at low temperatures, and a liquid crystal composition containing the same.